Hydrodynamic brake

ABSTRACT

The present invention relates to a hydrodynamic brake, which comprises a stator ( 1 ) and a rotor ( 2 ). The stator ( 1 ) and the rotor ( 2 ) are provided coaxially in relation to each other such the annular recesses ( 5, 10 ) of the stator ( 1 ) and the rotor ( 2 ) form a toroid-shaped space. A first medium is arranged to be supplied to said toroid-shaped space for providing a brake action during rotation of the rotor ( 2 ). The hydrodynamic brake comprises, with advantage, at least one injection member ( 16, 17 ), which is arranged to supply a second medium to the toroid-shaped space for reducing the circulation of air in the toroid-shaped space during time periods, when no brake action is desired. The second medium is supplied, at least one location, to the toroid-shaped space with a pressure and in a direction, which at least partly is directed towards the principal flow direction (a) of the circulating air.

BACKGROUND OF THE INVENTION AND PRIOR ART

[0001] The present invention relates to a hydrodynamic brake accordingto the preamble of claim 1.

[0002] In connection with the use of hydrodynamic brakes, such asretarders in vehicles, a certain brake action always arises during thepropulsion of the vehicle as a consequence of the rotation of the rotorwith a driving shaft of the vehicle. This brake action is caused by theair, which is located in the toroid-shaped space, being forced tocirculate. The circulating air provides in a corresponding way as theintroducable medium when it circulates in the toroid-shaped space abrake action. The supplied medium is usually an oil having suitableproperties. However, the density of the air is only a fraction of thedensity of the oil but the brake action arising hereby is not entirelynegligible. The fuel consumption of a vehicle having a retardertherefore becomes unnecessarily high.

[0003] In order to reduce this circulation of air in the toroid-shapedspace between the stator and the rotor, a plurality of differentsolutions have been proposed. A so-called dazzling-screen is for exampleused which is intended to be moved into the gap between the stator andthe rotor for preventing said circulation of air, when no brake actionis desired. The use of dazzling-screens includes a plurality of movablemechanical parts, which results in a complicated construction.

[0004] From EP 233 331 it is known to supply a blocking medium to thetoroid-shaped space of a retarder in order to reduce the circulation ofair and thus to reduce the brake action obtained by the circulating air.The blocking medium is supplied as a radially directed yet in thetoroid-shaped space. The intention is that the supplied blocking mediumhas to form a blocking medium curtain in the area between the stator andthe rotor in such a way that the circulation of air between the statorand the rotor is reduced. If the insertion of the medium here does nottake place with a sufficiently high velocity, the heavy circulation ofair, which may amount to 100 m/s in the toroid-shaped space, willrelatively quickly move the supplied blocking medium towards the wallsof the toroid-shaped space.

SUMMARY OF THE INVENTION

[0005] The object of the present invention is to provide a hydrodynamicbrake comprising means, which in a simple and effective way reduces thecirculation of air in the toroid-shaped space, which arises in thehydrodynamic brake when no brake action is desired to be obtained.

[0006] This object is achieved by the hydrodynamic brake of theinitially mentioned kind, which is characterised by the featuresmentioned in the characterising part of claim 1. By supplying the secondmedium with a high pressure and in a direction partly towards thecirculating air stream, a retardation of the velocity of the circulatingairflow is obtained, when the medium hits the circulating air. By thesupply of the medium with a suitably high pressure, it penetratesthrough the outermostly located air layer in the toroid-shaped space,which has the highest velocity. This is necessary for preventing thatthe medium, substantially immediately after it has been supplied, ismoved towards the walls of the toroid-shaped space by the outermostlylocated air stream. The second medium, which is supplied with apressure, is finely dispersed in the toroid-shaped space to a mediummist, which is retarding the velocity of the circulating air.

[0007] According to a preferred embodiment of the present invention, thesecond medium is arranged to be supplied in form of at least one jet.Said jet may have a suitable shape and a pressure, which activelyreduces the direction of motion and the velocity of the air. Such jetsought to be supplied with a velocity of above 10 m/s in order toguarantee that they will be able to retard and penetrate the outermostair layer in the toroid-shaped space. Preferably, the velocity ought tobe at least 20 m/s. Alternatively, the second medium may be supplied asa number of jets in order to obtain a more spread influence on thecirculating air in the toroid-shaped space. Advantageously, the secondmedium is identical with the first medium. The first medium is usuallyan oil. Such an oil is, in the most cases, also suitable as a medium forreducing the circulation of air in the toroid-shaped space. By using thesame medium for preventing said circulation of air as for providing abrake action, the handling of the second medium is simplified. Nospecial collecting containers for the medium need to be provided, forexample.

[0008] According to another preferred embodiment of the presentinvention, said means comprises at least one injection member, which isarranged to inject the second medium into the toroid-shaped space. Suchan injection member is arranged to supply the second medium into thetoroid-shaped space with a suitable pressure. The injection member mayalso comprise a suitable nozzle, which provides one or several jets witha suitable shape for reducing the circulation of air. The injectionmember may supply the second medium from a radially outwardly locatedportion of the toroid-shaped space. Thereby, the second medium may beinjected towards the circulating air in an area when the air flows fromthe rotor to the stator and has its highest velocity. Advantageously,the injection member supplies the second medium, in this case, via anorifice in a bottom surface of the recess of the stator. Since thestator is immobile, it is relatively uncomplicated to provide aninjection member in the stator for the supply of the second medium insaid area. In order to obtain an effective reduction of the velocity ofthe circulating air, the second medium ought to be supplied in adirection which has an angle of 15° to 45° to a radial direction, whichextends from the orifice of the injection member to a centre in thetoroid-shaped space. The circulating air is presumed to circulate roundabout in the toroid-shaped space along the bottom surfaces of therecesses of the stator and the rotor. Hereby, the principal flowdirection of the air becomes substantially perpendicular to such aradial direction. The more the supply direction of the medium deviatesfrom said radial direction the more contrary the medium hits thecirculating air stream. Advantageously, the second medium is supplied inone or several jets in a direction with an angle of 15° to 45° to saidradial direction. An angle of about 30° seems to be the most favourablein order to retard most effectively the velocity of the circulating airstream at the same time as a considerable part of the second medium maypass through this air stream and form a medium mist in the toroid-shapedspace.

[0009] According to another preferred embodiment of the presentinvention, said injection member may be arranged to inject the secondmedium from a radially inwardly located portion of the toroid-shapedspace. Hereby, the velocity of the circulating air is reduced in thepassage from the stator to the rotor. Advantageously, the injectionmember is, in this case, provided in a shaft portion of the rotor andcomprises an orifice in the bottom surface of the recess of the rotor.Advantageously, the second medium is supplied in a direction with anangle of 15° to 45° to a radial direction, which extends from theorifice of the injection member to a centre in the toroid-shaped space.Supplying jets with a high pressure in an angle range of about 30° seemsto be the most favourable for in the most efficient manner retarding thecirculating air stream at the same time as an effective medium mist isobtained in the toroid-shaped space. Suitably, said means comprises aplurality of injection members located both at radially outwardly andinwardly located portions and with constant intervals along the circularextension of the toroid-shaped space. Thereby, the circulation of airmay be counteracted effectively in the whole toroid-shaped space.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the following a preferred embodiment of the invention isdescribed as an example with reference to the attached drawings, inwhich:

[0011]FIG. 1 shows a cross section through a portion of a hydrostaticbrake according to the present invention,

[0012]FIG. 2 shows separately the stator showed in FIG. 1 and

[0013]FIG. 3 shows separately the rotor showed in FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION

[0014]FIG. 1 shows a cross section through a portion of a hydrodynamicbrake in form of a retarder of a motor driven vehicle. The retardercomprises a stator 1 and a rotor 2. The stator 1, which is shownseparately in FIG. 2, comprises a body having an inner radial surface 3,which defines a circular opening. A rotatable shaft 4 is arranged toextend through the circular opening of the stator 1. The rotatable shaft4 is, via a transmission device, in connection with a driving shaft ofthe vehicle. The stator 1 is fixedly provided in the vehicle in asuitable way. The body of the stator 1 comprises an annular recess 5,which in the mounted state of the retarder, extends around the rotatableshaft 4. The annular recess 5 is restricted in a radial directionoutwards by an outer edge 6 and in a radial direction inwards by aninner edge 7. A number of vanes 8 are provided with uniform intervalsalong the circular extension of the annular recess 5. The vanes 8 have asubstantially radial extension through the recess 5 from its inner edge7 in a direction towards its outer edge 6. The lateral surfaces of thevanes 8 have an angle of about 45° in relation to the bottom surface ofthe recess 5.

[0015] The rotor 2, which is shown separately in FIG. 3, comprises abody with a shaft portion 9, which is fixedly connected to the rotatableshaft 4. Thereby, the rotor 2 will rotate synchronously with therotatable shaft 4. The rotor 2 moreover comprises a substantiallycorresponding construction as the stator 1 and comprises an annularrecess 10, which extends around the rotatable shaft 4 in the mountedstate of the rotor 2. The annular recess 10 is restricted in a radialdirection outwards by an outer edge 11 and in a radial direction inwardsby an inner edge 12. A plurality of vanes 13 are provided with uniformintervals along the circular extension of the annular recess 10. Thevanes 13 have a substantial radial extension through the recess 12 fromits outer edge 11 in a direction towards its inner edge 12. Each of thelateral surfaces of the vanes 12 has an angle of about 45° in relationto the bottom surface in the recess 10.

[0016] The stator 1 and the rotor 2 are coaxially provided in relationto each other around the shaft 4 in such a way that the annular recesses5, 10 of the stator 1 and the rotor 2 together form a toroid-shapedspace, which extends around the rotatable shaft 4. The stator 1comprises a plurality of openings 14 through which a medium, in form ofan oil, is introduceable to the toroid-shaped space when the vehicle isintended to be braked. The supplied oil is guided, during the rotationof the rotor 2, by the vanes 13 in the direction of rotation andradially outwards in the toroid-shaped space along the bottom surface ofthe recess 10 and is thrown with a high velocity from the outer edge 11of the recess 10 of the rotor 2 over to the outer edge 6 of the recess 5of the stator 1. The direction of rotation of the oil in thetoroid-shaped space is shown by the arrows a in FIG. 1. The oil hits thevanes 8 of the stator 1 and the motion of the oil in the direction ofrotation of the rotor 2 is retarded and the oil is guided by the vanes 8radially inwards along the bottom surface of the recess 5 until itreaches the inner edge 7 of the recess 5. Here, the oil again is thrownover to the rotor 2 and hits the rotor 2 at the inner edge surface 12 ofthe recess 10. The oil hits the rotating vanes 13 of the rotor 2 at anangle in such a way that a substantially optimal brake action isobtained by the rotor 2. Thereafter the oil is guided by the rotatingvanes 13 at the same time as it is guided radially outwards along thebottom surface of the recess 10. The brake action obtained by the rotor2 depends partly on the quantity of oil which is supplied and iscirculated in the toroid-shaped space and partly on the rotary speed ofthe rotor 2. During the braking process, the kinetic energy of the oilis transformed to heat energy. The stator 1 comprises a number ofopenings 15 through which the oil is arranged to be removed from thetoroid-shaped space, when a brake action is not any longer desired.

[0017] In a corresponding way as the circulating oil supplies a brakeaction to the rotor, a circulation of the existing air in thetoroid-shaped space supplies a brake action. Said circulation of air isa problem when no brake action is desired. Since the air has a muchlower density than oil, the brake action, which is supplied by thecirculating air, becomes considerably lower than the one provided by theoil. However, the supplied brake action is not entirely negligible andresults in, for example, at the propulsion of a motor vehicle, anunnecessarily high fuel consumption.

[0018] In order to counteract such a circulation of air, a firstinjection member 16 has been provided at an outer portion of the stator1. The first injection member 16 is arranged to supply a second medium,which with advantage is identical with the oil used for obtaining abrake action in the retarder. The first injection member 16 supplies thesecond medium by one or several jets, which are supplied with a highpressure in such a way that the medium obtains an initial velocity ofabout 20 m/s. The jets are arranged to be injected in a direction whichdeviates with an angle v₁ of about 30° to a radial direction r₁, whichextends from the orifice of the injection member 16 and through a centrec in the toroid-shaped space. The principal air stream obtains acorresponding flow direction a as the oil. Consequently, the air streamfollows substantially the bottom surfaces of the toroid-shaped space inthe stator 1 and the rotor 2. Thus, the substantial flow direction a ofthe air becomes in the injection area substantially perpendicular tosuch a radial direction r₁. The larger angle, at which the second mediumis supplied to the toroid-shaped space, to said radial direction, themore contrary the medium hits the circulating air stream. However, theinjection angle v₁ may be varied within a range from 15° to 45°. Theinjected second medium counteracts here the passage of the air from therotor 2 to the stator 1 before it forms a medium mist in thetoroid-shaped space.

[0019] A second injection member 17 is provided in a shaft portion 9 ofthe rotor 2 and comprises an orifice in the bottom surface of the recess10 of the rotor 2. The second injection member 17 is arranged to supplythe second medium by a plurality of jets with a high pressure. The jetsare arranged to be injected in a direction which deviates with an anglev₂ to a radial direction r₂, which extends from the orifice of theinjection member 17 and through said centre c in the toroid-shapedspace. However, the injection angle v₂ may be varied within a range from15° to 45°. The injected medium counteracts here the passage of the airfrom the stator 1 to the rotor 2 before it forms a medium mist in thetoroid-shaped space.

[0020] The first 16 and the second 17 injection members are provided sothat the injected second medium first of all has to reduce the velocityof the air during the passage between the stator and rotor in one of thedirections. Here, the velocity of the air may be substantiallyconsiderably reduced by supplying the medium with a high velocity in adirection partly towards the flow direction a of the air. By supplyingthe jets with a high velocity, the medium passes principally through atleast the outermost air layer and obtains a spreading such that a mediummist of small finely dispersed medium droplets are formed, which furthercounteract the circulation of air between the stator and the rotor inthe toroid-shaped space. However, the formed oil droplets are graduallymoved towards the bottom surface of the recess 5, 10 of the stator 1 orthe rotor 2, whereafter the oil is guided out. The first 16 and second17 injection members are with advantage provided at constant intervalsalong the extension of the toroid-shaped space for counteracting thecirculation of air between the stator 1 and the rotor 2 along the wholeextension of the toroid-shaped space.

[0021] The present invention is not in any way restricted to the aboveembodiment described in the drawings but may be modified freely withinthe scopes of the claims.

1. Hydrodynamic brake comprising a stator (1) and a rotor (2) which eachcomprises a body having an annular recess (5, 10) and a plurality ofvanes (8, 13) provided in the respective recesses (5, 10) of the stator(1) and the rotor (2), wherein the stator (1) and the rotor (2) areprovided coaxially in relation to each other in such a way that theannular recesses (5, 10) of the stator (1) and the rotor (2) form atoroid-shaped space, a first medium arranged to be supplied to saidtoroid-shaped space for providing a brake action during rotation of therotor (2), and means arranged to supply a second medium to thetoroid-shaped space during time periods, when no brake action isdesired, for reducing the circulation of air in the toroid-shaped space,characterised in that said means is arranged to supply the secondmedium, at at least one location, to the toroid-shaped space with apressure and in a direction which at least partly is directed towardsthe principal flow direction of the circulating air (a).
 2. Hydrodynamicbrake according to claim 1, characterised in that the second medium isarranged to be supplied in form of at least one jet.
 3. Hydrodynamicbrake according to claim 1 or 2, characterised in that the second mediumis identical with the first medium.
 4. Hydrodynamic brake according toany one of the preceding claims, characterised in that said meanscomprises at least one injection member (16, 17) which is arranged toinject the second medium into the toroid-shaped space.
 5. Hydrodynamicbrake according to claim 4, characterised in that said injection member(16) is arranged to supply the second medium from a radially outwardlylocated portion of the toroid-shaped space.
 6. Hydrodynamic brakeaccording to claim 5, characterised in that said injection member (16)supplies the second medium via an orifice in a bottom surface of therecess (5) of the stator (1).
 7. Hydrodynamic brake, according to claim6, characterised in that the second medium is supplied in a directionwith an angle (v₁) between 15° to 45° to a radial direction (r₁), whichextends from the orifice of the injection member (16) and through acentre (c) in the toroid-shaped space.
 8. Hydrodynamic brake accordingto claim 4, characterised in that said injection member (17) is arrangedto inject the second medium from a radial by inwardly located portion ofthe toroid-shaped space.
 9. Hydrodynamic brake according to claim 7,characterised in that said injection member (17) is provided in a shaftportion (9) of the rotor (2) and comprises an orifice in the bottomsurface of the recess (10) of the rotor (2).
 10. Hydrodynamic brakeaccording to claim 9, characterised in that the second medium issupplied in a direction which deviates with an angle (v₂) between 15° to45° to a radius (r₂), which extends from the orifice of the injectionmember (17) and through a centre (c) in the toroid-shaped space.